Photographic lens system

ABSTRACT

WHERE F THE FOCAL LENGTH OF THE LENS SYSTEM; Rho D THE TOTAL THICKNESS OR DIMENSION ALONG THE OPTICAL AXIS OF THE SYSTEM; D1 THE THICKNESS OF THE FIRST OR POSITIVE SINGLE MENISCUS LENS; R2 THE RADIUS OF CURVATURE OF THE CONCAVE SURFACE OF THE FIRST LENS; R6 THE RADIUS OF CURVATURE OF THE LAST REFRACTING SURFACE OF THE SYSTEM; N1 THE INDEX OF REFRACTION OF THE FIRST LENS (FOR THE D LINES OF HELIUM); AND N3 THE INDEX OF REFRACTION OF THE THIRD OR BICONVEX LENS (FOR THE D LINES OF HELIUM).   A photographic lens system in which a stop may be positioned in an image space adjacent to the last refracting surface of the system. Three individual lenses are included, i.e., a positive single meniscus lens with its convex surface toward an object, a biconcave lens and a biconvex lens. The following relations are satisfied:

U llltCu Dl'c Kamimura X WIID PHOTOGRAPHIC LENS SYSTEM Inventor: Hqilme Kamirnura, Tokyo, Japan Ricoh Co., Ltd., Tokyo, Japan Apr. 15, 1970 Assignee:

Filed:

Appl. No.:

Foreign Application Priority Data Apr. 17, 1969 Japan ..44/29923 us. Cl ..350/226, 350/206 Int. Cl ..G02b 9/16, G02b 9/08 Field of Search ..350/226, 206, 210

References Cited UNITED STATES PATENTS Reiss ..350/226 X Herzberger ..350/226 Primary ExaminerDavid Schonberg Assistant Examiner-Paul A. Sacher Attomey-Henry T. Burke, Robert S. Dunham, P. E. Henninger, Lester W. Clark, Gerald W. Griffln, Thomas F. Moran, R. Bradlee Boal, Christopher C. Dunham and Robert Scobey 1 Mar. 14, 1972 ABSTRACT A photographic lens system in which a stop may be positioned in an image space adjacent to the last retracting surface of the system. Three individual lenses are included, i.e.. a positive single meniscus lens with its convex surface toward an object, a biconcave lens and a biconvex lens. The following relations are satisfied:

where f=the focal length of the lens system; 2d=the total thickness or dimension along the optical axis of the systems d,=the thickness of the first or positive single meniscus lens; r =the radius of curvature of the concave surface of the first lens; r =the radius of curvature of the last refracting surface of the system; n =the index of refraction of the first lens (for the d lines of helium); and n =the index of refraction of the third or biconvex lens (for the d lines of helium).

gear, 2 Drawing Figures Patented March 14, 1972 3,649,103

FIG. 2

SPHERICAL ABERRATION ASTIGMATISM DISTORTION -v+ 0.0l 0 001mm -0.0l 0 00mm. -2 O INVENTOR H/lJ/ME KAM/MUAA BACKGROUND OF THE INVENTION The present invention relates to a photographic lens system. and more particularly a photographic lens system in which a stop or diaphragm may be positioned in an image space adjacent to the last refracting surface of the system.

In a conventional lens system consisting of three or four lenses, a stop or diaphragm is interposed between the first and second lenses or between the second and third lenses. When a stop or diaphragm is disposed behind the last refracting surface of the lens system in the image space, incident rays forming a relatively large angle with the optical axis of the lens system are cut out or vignetted as the diaphragm is stopped down, so that less light is directed to the edge of the field than to the center. This results in a serious problem when such a lens system is used for photographic purposes.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an improved photographic lens system in which a stop or diaphragm may be positioned in the image space adjacent to the last refracting surface of the system.

It is another object of the present invention to provide an improved photographic lens system which effectively eliminates vignetting.

It is a more specific object of the present invention to provide an improved photographic lens system of the character described above with an aperture ratio of l 2.8 and a field angle of 54.

The present invention involves a lens system formed from a plurality of lens elements. It has been discovered that in order to eliminate vignetting in such a lens system, the following relation must be satisfied.

0.3 f 2d 0.35fwhere f= the focal length of the lens system; and pa the total thickness or dimension of the lens system along the optical axis thereof.

Furthermore, it has been discovered that the spherical aberration of such a lens system can be well balanced when the following condition is satisfied:

0. l05f d, O.l f where d the thickness of the first lens element of the system facing toward an object.

When pd is too small, a lens system of the character described cannot be achieved physically. On the other hand, when d is too large, vignetting cannot be sufficiently eliminated. In order to obtain a better image, it has been found that the following conditions must be also satisfied so as to balance the astigmatism as well as coma caused by the above described conditions:

r the radius of curvature of the surface of the first lens element of the system opposite from the surface facing an object; and

"a the radius of curvature of the last refracting surface of the system facing the image plane of the system.

It has also been found that the following conditions must be satisfied for more advantageously correcting the Petzval sum and balancing curvature of field:

1.65 n where n, and n are the indices of refraction of the first and third lens elements of the system for the d lines of helium.

When the above conditions are satisfied, a photographic lens system with an aperture ratio of l 2.8 and a field angle of 54 may be provided in which a stop or diaphragm can be positioned in the image space adjacent to the last refracting surface of the lens system and all of the optical aberrations are well balanced.

The above and other objects, features and advantages of the present invention will become more apparent from two exam- 1 pics described hereinafter with reference to the accompanying .drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a diagrammatic side view of one embodiment of the present invention; and

FIG. 2 is a graph showing aberration curves thereof.

DETAILED DESCRIPTION In FIG. 1 a triplet lens system in accordance with the invention is shown. A first positive single meniscus lens element 1. is included, having a convex surface facing toward an object (not shown) and a concave surface 101:. Also included are a second lens element 11 comprising a biconcave lens with, concave surfaces Ila and 11b, and a third or last lens element 12 comprising a biconvex lens with convex surfaces and 12b. The surface 12b constitutes the last refracting surface of the lens system and faces toward an image plane (not shown). A stop or diaphragm 13 may be positioned in the image space adjacent the last refracting surface 12b.

The parameters of the lens system of FIG. I are as follows: r the radius of curvature of the convex surface 10:: facing toward an object of the first positive meniscus lens 10; r the radius of curvature of the concave surface 10b of the meniscus lens 10; r and r, the radii of curvature of the concave surfaces He and 11b of the second biconcave lens 11; r and r, the radii of curvature of the convex surfaces 12a and 12b of the the third biconvex lens 12; d the thickness of the first positive meniscus lens 10 along the optical axis 9 of the lens system; d the length of the air space between the first and second lenses l0 and 11 meaured along the optical axis 9; d the thickness of the second lens 11 measured along the optical axis; 1L the length of the air space between the second and third lens 11 and 12 measured along the optical axis 9; d the thickness of the third lens I2 measured along the optical axis; n, the index of refraction of the first lens [0 for the d lines of helium; n the index of refraction of the second lens 11 for the d lines of helium; n the index of refraction of the third lens 12 for the d lines of helium; yd, the Abbe number of the first lens 10 for the :1 lines of helium; 7d, the Abbe number of the second lens 11 for the d lines of helium; and yd, the Abbe number of the third lens 12 for the d lines of helium. Two examples are given below of lens systems in accordance with the invention.

position of a stop or diaphragm of Example I are as follows:

Coefficient Coefficient of sphercal Coefficient of astig- Petzval Coefficient aberration of coma matism coefficient of distortion 1 (surface a) 7.11399 0.20460 0.00588 1.24119 0.03587 2 (surface 10b) 0.00086 0.02174 0.54609 0.58961 1.09254 3 (surface 11a) 3.63508 2.59215 1.84844 0.44856 1.63796 4 (surface 1 lb) 8.78l83 2.48867 0.70526 1.16718 0.53063 5 (surface 122:) 3.02298 1.64224 0.89215 0.65007 0.83783 6 (Surface 12b) 4.13406 2.08016 1.04669 0.65009 -0.85378 2 (lens system) 1.85498 0.10810 0.33600 0.03471 Spherical aberration. astigmatism and distortion curves are toward an object of the first positive meniscus lens;

shown in FIG. 2. Spherical aberration is plotted in terms of 15 r, the radius of curvature of the concave surface of the mm as a function of aperture ratio. Astigmatism is plotted in meniscus lens; terms of mm. as a function of field angle. Distortion is plotted r;, and r the radii of curvature of the concave surfaces of in terms of percent as a function of field angle. the second biconcave lens;

EXAMpLE 2 r and r the radii of curvature of the convex surfaces of the third biconvex lens;

d the thickness of the first positive meniscus lens along k' the optical axis of the lens system; $3252 3: :2 d the length of the air space between the first and second d 7d 7 lenses measured along the optical axis;

d the thickness of the second lens measured along the op tical axis; 2-32:3; 13:52:; :32 1:23;: d the length of the air space between the second and third r,=0.967f d,=o.o24 n,=|.696so yd,=55.6 lenses measured along the optical axis; 0.320 d.=0.057f d the thickness of the third lens measured along the optir 0.774 a,=o.oso cal axis; "guns, n, the index of refraction of the first lens for the 4' lines of Seidel coefficients of aberrations in consideration of the m i h e index of refraction of the second lens for thedlines position of a stop or diaphragm of Example 2 are as follows: of helium;

Coefficient Coefficient of sphercal Coefficient of astig- Eetzval Coefficient aberration of coma matism coefficient of distortion 1 (surface 10a) 7.31772 0.18999 0.00493 1.26080 0.03286 2 (surface 10b) 0.01035 0.08464 0.69218 0.54730 1.18490 3 (surface 11a) 3.69304 2.70201 1.97693 0.38497 1.72806 4 (surface 11b) 7.32593 2.04032 0.56824 1.16098 0.48160 5 (surface 12a) 1.61902 1.08157 0.72254 0.53019 0.83689 6 (surface 4.11095 2.07698 1.04935 0.63874 0.85288 E (lens system) 2.03907 0.22837 0.07617 0.33648 0.07843 What is claimed is: n;, the index of refraction of the third lens for the d lines of 1. A photographic lens system suitable for the inclusion ofa helium, stop in an image space adjacent to the last refracting surface 7 h Abbe number of the first lens for the d of of the system and having an equivalent focal length of about h i m; 1.0 and an aperture ratio of about 122.8 and a field angle of 7 the Abbe number of the Second lens for the 4 lines of about 54, comprising three individual lens elements, the first helium; and lens element comprising a positive single meniscus lens with 55 7 =-the Abbe number of the thud lens for the d hhes 0f its convex surface toward an object; the second lens element hehumcomprising a biconcave lens; the third lens element comprising a biconvex lens having a refractive surface facing the image plane; and said lens system substantially satisfying the following relations:

range ofr range ofd range ofn range of 7d -romoo to 1.67790 n,=1.59270 n,=l 119350 in 1.69680 2. A photographic lens system according to claim 1, in which the values of r, d, n and ya are as follows:

3. A photographic lens system according to claim 1. in which the values of r, d, n and a are as follows: 

1. A photographic lens system suitable for the inclusion of a stop in an image space adjacent to the last refracting surface of the system and having an equivalent focal length of about 1.0 and an aperture ratio of about 1:2.8 and a field angle of about 54*, comprising three individual lens elements, the first lens element comprising a positive single meniscus lens with its convex surface toward an object; the second lens element comprising a biconcave lens; the third lens element comprising a biconvex lens having a refractive surface facing the image plane; and said lens system substantially satisfying the following relations: range of rrange of d r1 0.323f to 0.320fd1 0.110f to 0.105f r2 0.680f to 0.738f d2 0.057f to 0.048f r3 -0.830f to -0.967f d3 0.026f to 0.024f r4 0.319f to 0.320f d4 0.046f to 0.057f r5 0.630f to 0.774f d5 0.078f to 0.080f r6 -0.630f to -0.643f range of nrange of gamma d n1 1.67000 to 1.67790 gamma d1 57.3 to 55.5n2 1.59270 gamma d2 35.4 n3 1.69350 to 1.69680 gamma d3 53.4 to 55.6 where: r1 the radius of curvature of the convex surface facing toward an object of the first positive meniscus lens; r2 the radius of curvature of the concave surface of the meniscus lens; r3 and r4 the radii of curvature of the concave surfaces of the second biconcave lens; r5 and r6 the radii of curvature of the convex surfaces of the third biconvex lens; d1 the thickness of the first positive meniscus lens along the optical axis of the lens system; d2 the length of the air space between the first and second lenses measured along the optical axis; d3 the thickness of the second lens measured along the optical axis; d4 the length of the air space between the second and third lenses measured along the optical axis; d5 the thickness of the third lens measured along the optical axis; n1 the index of refraction of the first lens for the d lines of helium; n2 the index of refraction of the second lens for the d lines of helium; n3 the index of refraction of the third lens for the d lines of helium, gamma d1 the Abbe number of the first lens for the d lines of helium; gamma d2 the Abbe number of the second lens for the d lines of helium; and gamma d3 the Abbe number of the third lens for the d lines of helium.
 2. A photographic lens system according to claim 1, in which the values of r, d, n and gamma d are as follows: r d n gamma d r1 0.323f d1 0.110f n1 1.67000 gamma d1 57.3 r2 0.680f d2 0.057f n2 1.59270 gamma d2 35.4 r3 -0.830f d3 0.026f n3 1.69350 gamma d3 53.4. r4 0.319f d4 0.046f r5 0.630f d5 0.078f r6 -0.630f
 3. A photographic lens system according to claim 1, in which the values of r, d, n and gamma d are as follows: r d n gamma d r1 0.320f d1 0.105f n1 1.67790 gamma d1 55.5 r2 0.738f d2 0.048f n2 1.59270 gamma d2 35.4 r3 -0.967 d3 0.024f n3 1.69680 gamma d3 55.6. r4 0.320f d4 0.057f r5 0.774f d5 0.080f r6 -0.643f 